Optical system



y 1939- G. L. DiMMlCK 2,157,166

OPTICAL SYSTEM Filed Dec. 51, 1936- INVENTOR azz/v/vz, M/c/r Patented May 9, 1939 OPTICAL SYSTEM Glenn L. Dimmlck, Erlton, N. 1., assignor to Radio Corporation oi America, a corporation of Delaware Application December '31, 1936. Serial no. 118,429

This invention relates to improvements in optical systems and particularly to optical systems of the type used in recording sound on photographic film. The system involves a novel arrangement of cylindrical and spherical lenses for securingthe maximum light efiiciency in such a recording system.

Recording systems for making variable area sound records are well known in the art and the type thereof wherein a triangular aperture is imaged upon a slit and vibrated transversely across the slit is also known as shown, for example, in my Patent No. 1,999,721, issued April The present invention pertains to a somewhat analogous optical system having its various elements arranged along a V-shaped light path with the plane of this path perpendicular to the longitudinal axis of the film and with the one leg of the path perpendicular to the film. The arrangement of lenses herein disclosed, however, is entirely different from that shown in the aforesaid patent and isan improvement thereover in that it is more eflicient.

mask used.

The vibrating light beam from the galvanometer then passes through additional lenses to a. slit where a narrow lineof light is transmitted, which in turn is focused upon the film. These several lenses are all positive in power, and most of them are made cylindrical in order that the retracting power of the system, in either the vertical or the horizontal plane, may be made as effective as possible independent of the retracting power required in the plane perpendicular thereto.

By means of this arrangement of cylindrical lenses of proper focal lengths and spacings, it is possible (1) to direct a greater amount of light onto a galvanometer mirror than would otherwise be secured; (2) to produce a narrower line of light upon the film than could be conveniently secured by means of spherical lenses; (3) to reduce the length of the slit required to transmit the beam of light of appropriate shape, and thereby reduce the overall dimensions of the apparatus; and '(4) to fix the length of the line of light on the film, and the width thereof, in-

dependently of each other.

3 Claims.

(oi. ss-24) Qne object of my invention is to provide such an optical system which decreases the light losses in the system.

Another object of my invention is to provide such a system which uses primarily simple cylindrical lenses insofar as possible.

Another object of my invention is to provide such an optical system which gives an appropriate reduction in image size ineach plane.

Another object of my invention is to provide such an optical system which reduces the image of the illuminated slit much more in the longitudinal direction of the him than in the transverse direction of the film.

Another object of my invention is to produce such an optical system which will produce a very great reduction in the image of the optical slit in the direction of movement of the film without requiring an excessive length of the slit transversely of the film in order to secure proper soundtrack width.

Other and incidental objects of my invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which the single figure is a diagrammatic perspective view of my improved optical system.

Referring now to the drawing, the usual exciter lamp of the coil filament incandescent type is provided at 10. Light from the filament passes through the condenser lens ii which is a pianocylindrical lens having its axis vertical, 1. e., perpendicular to the plane of the V-shaped optical system. This lens condenses light from the lamp ill in the horizontal plane di to the galvanorneter' mirror I 6, the lens l5 which is also a planolens I.

This lens I4 is a double convex cylindrical lens with its axis horizontal and serves to condense the light from the lamp III in the vertical plane into the galvanometer mirror It.

After leaving the galvanometer mirror ii, the light passes again through the lens I! to the cylindrical lens H. The lens i'l, like the lens I, is a double convex cylindrical lens with its axishorizontal. The lenses i1 and H in cooperation form an image of the aperture I! in the vertical direction upon the slit plate l8, while the lens l5 which functions in the horizontal plane perpendicular to the plane of operation of the lenses I and I1 correspondingly defines the other outlines of theimage l0.

Assuming the mirror II to be vibrated about a horizontal axis in accordance with the sounds to be recorded, the image I 0 will be moved up and down across the aperture plate l8, thereby causing a greater or less portion of the triangular figure to fall on the slit which transmits a correspondingly long or short beam of light. The actuation of the galvanometer is preferably in the manner described in my aforesaid Patent No. 1,999,721. Light from the slit 20 passes through the lens 2|. As stated previously, the lenses Ii and I4 form an image of the filament of the lamp ID in the galvanometer mirror l6 and this lens 2! which is a convex spherical lens forms an image of this filament image in the lens 22. The lens 22 is a double convex cylindrical lens with its axis vertical and forms an image of the slit 20 on the film 24 at the point 25. This lens 22 is so chosen as to focal length that it will reduce the image of the illuminated portion IQ of the slit 20 in the ratio of 3 to l laterally of the film. It is, therefore, necessary with standard film using a sound-track .070" wide that the image I! have a maximum width of only .210" thereby permitting the use of a relatively short slot. The lens 23, however, which is a piano-convex cylindrical lens having its axis horizontal, is made of much shorter focal length than the lens 22 and provides a reduction of preferably 12 to l in the slit image in the direction of movement of the film since commercial practice at the present time requires the use of a slit width of from .0005" down to .00025". This permits the use of a slit 20 having a width of 12 times these dimensions which is' comparatively simple to construct, whereas a much narrower slit than this becomes extremely difficult of construction.

It will be apparent from the foregoing that the lenses are so chosen as to focal length and arranged in such sequence as to produce an extremely compact optical system of very high efllciency.

Having now described my invention, I claim:

1. An optical system of the class described including in sequence an exciter lamp, a cylindrical lens, a beam defining aperture plate, second and third cylindrical lenses, a galvanometer, a fourth cylindrical lens, a slit plate having a slit therein, a spherical lens and fifth and sixth cylindrical lenses, all arranged along a V-shaped path, the galvanometer being located at the apex of the V,'the first and third of said cylindrical lenses having their axes perpendicular to the plane of the V and having the exciter lamp and galvanometer mirror located at their conjugate fool, the second of said cylindrical lenses having its axis in the plane of the V and having the exciter lamp and galvanometer at its conjugate foci in said plane, the fourth of said cylindrical lenses having its axis in the plane of the V and having the said aperture plate and slit plate located at the conjugate foci of the second and fourth lenses perpendicular to said plane and at the conjugate foci of the third of. said lenses in said plane, and the fifth and sixth of said lenses having their axes respectively perpendicular to and parallel to said plane and having said slit plate and the final image plane of the optical system at their conjugate foci.

2. An optical system of the class described including in sequence an exciter lamp, a pianocylindrical lens, a beam defining aperture plate, second double and third plano-cylindrical lenses. a galvanometer, a fourth double cylindrical lens, a slit plate having a slit therein, a spherical lens and fifth and sixth cylindrical lenses, all arranged along a V-shaped path, the galvanometer being located at the apex of the V, the first and third of said cylindrical lenses having their axes perpendicular to the plane of the V and having the exciter lamp and galvanometer mirror located at their conjugate fool, the second of said cylindrical lenses having its axis in the plane of the V and having the exciter lamp and galvanometer at its conjugate foci in said plane, the fourth of said cylindrical lenses having its axis in the plane of the V and having the said aperture plate and slit plate located at the conjugate foci of the second and fourth lenses perpendicular to said plane and at the conjugate foci of the third of said lenses in said plane, and the fifth and sixth of said lenses having their axes respectively perpendicular to and parallel to said plane and having said slit plate and the final image plane of the optical system at their conjugate foci.

3. An optical system of the class described including in sequence an exciter lamp, a pianocylindrical lens having its cylindrical side toward said lamp, a beam defining aperture plate, second double and third piano-cylindrical lenses, a galvanometer, said third lens having its plano side toward and adjacent to the galvanometer, a fourth double cylindrical lens, a slit plate having a slit therein, a spherical lens and fifth and sixth cylindrical lenses, all arranged along a V- shaped path, the galvanometer being located at the apex of the v, the first and third of said cylindrical lenses having their axes perpendicular to the plane of the V and having the exciter lamp and galvanometer mirror located at their conjugate fool, the vsecond of said cylindrical lenses having its axis in the plane of the V and having the exciter lamp and galvanometer at its conjugate foci in said plane, the fourth of said cylindrical lenses having its axis in the plane of the V and having the said aperture plate and silt plate located at the conjugate fool of the second and fourth lenses perpendicular to said plane and at the conjugate foci of the third of said lenses in said plane, and the fifth and sixth of said lenses having their axes respectively perpendicular to and parallel to said plane and having said slit plate and the final image plane of the optical system at their conjugate foci.

,GLENN L. DIMMICK. 

